Wire spark chamber with magnetostrictive readout

ABSTRACT

A wire spark chamber having magnetostrictive readout. One embodiment thereof is for particular use with low energy gamma rays, X-rays, or neutral particles whose presence is detected by secondary particles produced in converters placed in or around the wire planes of the chamber. Another embodiment has a very large and uniformly sensitive detecting area by means of auxiliary conducting planes which serve to charge the chamber capacity with a low impedance transmission-line characteristic. The embodiment for use with low energy gamma, X-ray or neutral particles has utilization in the field of medical diagnostics while the large chamber embodiment provides the capability of detecting multiple tracks with uniform high efficiency, thus fulfilling a long looked for need in the field of wire spark chambers.

ililite States [72] Inventor Victor Perez-Mendez 3.373183 3/1968 Lansiart et a1. 250/83.1 (X) Berkeley, Calif. 3,449573 6/1969 Lansiart et a] 250/836 X 3, 2 5 1969 Primary Examiner-James W. Lawrence 3; 6 d 1971 Assistant ExaminerMorton J. Frorne i AIlrneyRoland A. Anderson [73] Asslgnee The United States of America as represented by the United States Atomic Energy Commission ABSTRACT: A wire spark chamber having magnetostrictive [54] WIRE SPARK CHAMBER WITH readout. One embodiment thereof is for particular use with MAGNETOSTRICTWE READOUT low energy gamma rays, X-rays, or neutral partlcleswhose 7 Claimsg Drawing Figs presence is detected by secondary partlcles produced ln converters placed in or around the wlre planes of the chamber. [52] US. Cl 250/83.6 R, Another embodiment has a very large and if l Sensitive 250/831 250/833 313/61 R detecting area by means of auxiliary conducting planes which [51] InLCl G01! /00 Serve to Charge the Chamber capacity with a low impedance [50] Field of Search 250/83.6, transmissiomline characteristia The embodiment f use with 313/61, 93 low energy gamma, X-ray or neutral particles has utilization in the field of medical diagnostics while the large chamber em- [56] Rem-"Ices Cited bodiment provides the capability of detecting multiple tracks UNITED STATES PATENTS with uniform high efficiency, thus fulfilling a long looked for 3,359,421 12/1967 Perez-Mendez et a1. 250/83.l (X) need in the field ofwire spark chambers.

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LINEAR PREAMPLIFIER AMPLIFIER 37 {-38 39 SPARK 1 CHAMBER I40 LOGIC PULSER INVENTOR. VICTOR PEREZMENDEZ W G. 624M.

ATTORNEY PAIENTEI] M824 en SHEU 2 [1F 2 spark Sense wire 80 &

Longiiudinol wuves D om in pad Damping pod E Ferromagnetic wire 87 Tronsmtting coil (86 Receiving coil dc S OURCE INVENTOR. VICTOR PEREZMENDEZ W. a. QM

AT TORNE Y WIRE SPARK CHAMBER WITH MAGNETOSTRICTIVE READOUT BACKGROUND OF THE INVENTION The invention described herein was made in the course of, or under, Contract No. W7405-ENG48, with the United States Atomic Energy Commission.

The use of wire spark chamber for localization of tracks of charged particles has proved to be a very useful tool in nuclear and elementary particle physics. In many experimental situations, the range and energy of the detected particles is suffrciently large so that the events are selected by a triggering signal derived from scintillation counters placed strategically around the spark chambers to form an appropriate coincidence for the event.

Such a prior triggering system is less effective in dealing with gamma rays or other neutral particles whose presence is detected by secondary charged particles produced in converters placed in or around the wire planes, and becomes very inefficient especially when dealing with low-energy gamma rays from radioactive sources or X-rays where the range of the secondary electrons is small enough so that they do not emerge from a single gap.

Also, these prior known wire chambers have been small, or where large wire chambers have been utilized the uniform efficiency thereof for registering multiple tracks has been low over the entire surface area, due to the large distributed inductances of the wire planes. In the prior known large wire chambers the longitudinal-mode magnetostrictive readout has dispersive characteristics which affect the shape of the acoustic pulses and require linearity corrections in order to achieve maximum accuracy.

SUMMARY OF THE INVENTION The invention relates generally to spark chambers for detecting radiation and particularly to a wire spark chamber which in one embodiment has a self-triggering means for use with low energy, neutral particles, and in another embodiment has large plane surfaces which have highly uniform sensitivity thereover. Thus the present invention overcomes the problems of the prior known wire chambers in the detection of low energy gamma rays, Xrays, or neutral particles whose presence is detected by secondary particles, and in uniform efficiency for registering multiple tracks with large chambers. Each embodiment utilizes a magnetostrictive readout, with the readout for the large chamber embodiment utilizing torsional pulses in the sense wire which provide a greater degree oflinearity than the longitudinal pulses used previously.

Therefore, it is an object of this invention to provide an im proved wire spark chamber with magnetostrictive readout for detecting radiation.

A further object of the invention is to provide an ionizationtriggered wire chamber with magnetostrictive readout for detecting low energy, neutral particles.

Another object of the invention is to provide a self-triggering wire spark chamber having magnetostrictive readout for particular use with low energy gamma rays, X-rays, or neutral particles whose presence is detected by secondary particles.

Another object of the invention is to provide a wire spark chamber for detecting radiation which has a very large plane surface which has highly uniform sensitivity thereover.

Another object of the invention is to provide a large spark chamber which utilizes torsional pulses in the magnetostrictivc readout.

Other objects of the invention will become readily apparent from the following description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of the detection of low energy gamma rays by secondary charged particles produced in converters placed in or around the wire planes of the spark gap;

FIG. 2 is a schematic diagram of an embodiment for gas multiplication triggering of a spark chamber in accordance with the invention;

FIG. 3 is a schematic diagram of a magnetostrictive chamber with independent gaps;

FIG. 4 is a schematic diagram of a sparkostrictive chamber with common high-voltage plane;

FIG. 5 is a schematic diagram of an artificial charging line;

FIG. 6 diagrammatically illustrates the generation of torsional pulse by summation of steady-state azimuthal field and pulsed longitudinal magnetic field;

FIG. 7 illustrates a mode converter for the detection of torsional pulses; and

FIG. 8 illustrates schematically a no nbiased coil for the detection of torsional pulses.

DESCRIPTION OF THE EMBODIMENTS Referring now to the drawings, FIGS. 1 and 2 illustrate an embodiment of the invention comprising a self-triggering wire spark chamber having magnetostrictive readout for particular use with low energy gamma rays, X-rays, or neutral particles whose presence is detected by secondary particles produced in converters placed in or around the wire planes of the chamber. Normally, the spark chamber is utilized as a proportional counter wherein the ionization currents produced in the primary avalanches are picked up by a high-voltage plane of the chamber. These proportional pulses are then amplified and applied to a logic circuit which controls activation of the spark chamber pulser. The resulting sparks at the secondary particle locations are then detected by a conventional mag netostrictive readout system.

As pointed out previously, the prior known triggering systems for wire spark chambers have been effective where the range and energy of the detected particles are sufficiently large so that the events are selected by a triggering signal derived from scintillation counters. However, such triggering systems are less effective in dealing with gamma rays or other neutral particles whose presence is detected by secondary charged particles produced in converters placed in or around the wire planes of the chamber, as illustrated in FIG. 1 described hereinafter, and becomes very inefficient especially when dealing with low-energy gamma rays from radioactive sources or X-rays where the range of the secondary electrons is small enough so that they do not emerge from a single gap. As illustrated in FIG. 1 a wire spark chamber generally indicated at 10 consists ofa plurality of wire planes 11 and has a lead (pb) converter 12 positioned on one side of chamber 10 with a scintillator 13 positioned on the opposite side thereof. Gamma y rays 14 which penetrate converter 12 are converted to secondary charged particles, converted electrons 15, produced in converter 12 which are detected by scintillator 13. The detection of the converted electrons 15 by scintillator 13 gives rise to a logic signal that is used to trigger the wire spark chamber 10.

In view of the interest in using wire chambers for medical diagnostic purposes for the localization of gamma-emitting radioactive isotopes with energy ranging from a few kev. to l Mev. the investigation of the characteristics of the signals produced by low-energy charged particles in the preavalanche region in the wire chamber and the sparking characteristics of the chamber itself when triggered by these signals has resulted in the system illustrated in FIG. 2 and described hereinafter. The basic feature ofthe inventive concept illustrated in FIG. 2 is that the ability to read out spark coordinates electrically by magnetostrictive delay-line methods is preserved so that the ease of handling and computing large numbers of events is retained. in this respect, the present invention differs from other work in which some form of self-triggering methods are used and the sparks are subsequently photographed.

An embodiment of the inventive spark chamber and as sociated circuitry for utilization with low energy, neutral particles is illustrated in FIG. 2, the wire spark chamber being indicated generally at 20. Such a chamber embodiment was utilized to test the properties of gas-multiplication triggering, and, for example, has an active area of cm. by 20 cm. and a capacity of I40 pf. Chamber 20 consists of three planes 21, 22 and 23, the central plane 21 being made by stringing 0.08 mm. steel wires l mm. apart over a lucite frame. The outside planes 22 and 23 are of copper-plated mylar. etched in strips 1 mm. wide, 1 mm. apart. The distance between the center plane 21 and outside planes 22 and 23 is 1 cm. in each case, and magnetostrictive readout is possible from all three planes. For operation, the chamber 20 is filled at atmospheric pressure with a 90 percent Ne 10 percent He gas mixture saturated at room temperature 18 c) with ethyl alcohol 40 mm. Hg.).

The circuitry of FIG. 2 used for particle detection and spark triggering consists of the outer planes or electrodes 22 and 23 being connected to ground with a positive high voltage from power supply or source 24, for example, 3900 volts, is applied to the central plane or electrode 21 via lead 25. A resistor 26, 22 M ohms for example, is used in lead 25 to limit the current available to the chamber 20 and prevent a continuous discharge. The resistor 26 also determines the recovery time of the chamber for detection of particles after sparking since it limits the recharging rate of the chamber. The proportional pulses are collected from the high-voltage electrode or plane 21 through lead 25, a capacitor 27, of 100 pf. for example, in a lead 28 into a voltage-sensitive preamplifier 29 having an input impedance, for example, of 10 k. ohms. The preamplifier has a gain of about 20 and its pulses are fed via a lead 30 into a variable-gain linear amplifier 31, having a gain of about 500 for example. The preamplifier 29 is protected during sparking by a simple back-to-back diode arrangement positioned in lead 28 and generally indicated at 32, with a resistor 33, of l K. ohms, for example, to limit the current through the diodes 32. The spark chamber 20 is decoupled by a series gap 34 from the capacitor 27 in the high-voltage pulsing system, series gap 34 being connected to high-voltage lead 25 atpoint 35 via a lead 36 which is also connected to a spark chamber pulser 37. The output from amplifier 31 is connected by lead 38 to a logic circuit 39, the output of which is directed to pulser 37 via lead 40. To eliminate ripple in the power supply 24, a capacitor 41, 4000 pf. for example, is connected via a lead 42 to lead 25 intermediate power supply 24 and current limiting resistor 26, the lead 42 also being connected to ground. A resistor 43 positioned in a lead 44 is connected to lead 42 and to lead 28 intermediate capacitor 27 and resistor 33 to provide a resistive ground connection.

When the chamber 20 is operated with the gas mixture as above described, about 0.25 mv. pulses are obtained for an ap-- plied voltage of 3900 v, this corresponding to a gas amplifica-- tion of approximately 6000.

The detection efficiency to the chamber 20 was tested by placing it between two scintillation detectors and counting simultaneously double (between the scintillators only) and triple coincidences. The results, as a function of applied DC voltage, showed, the efficiency of the gas multiplication triggered spark chamber to be satisfactory.

In tests where the high-voltage sparking pulses were supplied using a variable threshold discriminator set to trigger at. 10 percent of the height of the average pulses, it was found that the chamber 20 fired about 0.4 usec. after passage of the particle through the chamber. Since no appreciable losses in sparking efficiency were found for times up to 0.5 usec. after passage of the particle, the delay can be tolerated. It was found that the triggering jitter time was less than 0.3 sec. Also, it was observed that the operation of the chamber was moderately insensitive to the rise time of the high-voltage pulse and that rise times of about nsec. did not cause any loss in efficiency.

Also measured with satisfactory results was the rekindling time of chamber 20 (time needed for a spark to be formed along the path ofa previous spark, i.e., the number of double sparks on the same track as a function of the delay time between the sparks).

All the characteristics of the chamber 20 (memory time, jitter time, rekindling time, proportional pulse shape, etc.) are functions of many parameters of which the most important are: the type of gas in the chamber, the type and concentration of quenching agent (ethanol, methanol, etc.), the high voltage used for the proportional pulses which influences the sparking conditions, the energy in the sparks, the spark decay time. These parameters can be optimized for the particular requirements needed from the chambers.

In the prior art devices, when imaging single gamma ray emitting nuclei, a collimator was placed between the source and the converter and for all practical applications, the resolution of the system is given by the whole configuration of the collimator which has the main limiting effect on the sensitivity of the system, depending on the scattered radiation background that is tolerably and on the collimator material. Such prior known chamber is to be triggered on all counts in the scintillator except the ones blocked by an associated cosmic-ray anticoincidence counter. In these prior systems not all triggers correspond to real events since an appreciable number of gamma rays will convert in scintillator itself giving rise to false triggers, and conversely, not all electrons reaching the chamber give rise to a trigger signal. It is in this type of application where full advantages of the inventive gas-multiplication-triggered spark chambers are realized, since the chambers allow for detection of particles that would not register otherwise, and an increase in detection efficiency produces a directly-proportional increase in sensitivity. It is generally the case that data collection is sensitivity-limited rather than spark chamber recovery-time-limited, so that the benefit of inventive gas-multiplication triggering is that it allows for an increase of data collection rates through improved sensitivity.

It is thus seen that the embodiment illustrated in FIG. 2 provides a substantially improved wire spark chamber having selftriggering means and which is particularly adapted for use with low energy, neutral particles.

Referring now to the embodiment of the invention illustrated by FIGS. 3-8 which comprises a wire spark chamber providing highly uniform sensitivity over very large chamber plane surfaces. Thin auxiliary conducting planes are placed close to the wire planes to charge the capacity of the chamber gaps with a low impedance transmission-line characteristic. A low impedance matching termination between the auxiliary planes insures uniform electric field in the gap during spark buildup and the total spark current drawn may be limited by use of a quenching gas. Voltage pulses on the chamber gaps are provided by the discharge of a matched impedance delay line. Thus a high uniform efficiency for registering multiple tracks is obtained. In addition a uniform current is passed through the sensing wire to produce a steady state azimuthal magnetic field which, when combined with the local longitudinal field of spark, produces a local helical field and generates a torsional mode pulse along the wire by means of the Wiedemann effect, thereby eliminating the dispersive propagation problems of conventional longitudinal pulsing of long length sensing wire. Since torsional pulses, when traveling down a long wire, do not have the tendency to spread that longitudinal pulses have, the definition of a pulse generated a long distance from the pulse sensors is preserved, thereby improving the magnetostrictive readout due to the greater degree of linearity provided by the torsional pulses.

In many spectrometer-type experiments in which wire chambers with magnetostrictive readout have been used, a conventional cross-wire arrangement for small wire chambers has been utilized. Based on the success of this prior technique, the wire chamber has been modified for use in large chambers capable of detecting multiple tracks with a uniform high efficiency. As regards the stereo ambiguity problems, it has been found that these are essentially resolved by making the inventive chambers in modules of two gaps, with each gap forming an independent set of coordinates. These wire plane arrangements, however, have the difficulty that direct pulsing of the chambers does not produce a very uniform efficiency over the entire sensitive area due to the large distributed inductances of the wire planes. This difficulty has been resolved by the inventive chamber by providing additional thin aluminum planes which are used to charge the capacity of the chamber gap with a characteristic approximating that of a transmission line. A second difficulty that occurs in the readout when the prior known chambers become large enough in any one dimension (more that 2 or 3 meters) is that the longitudinalmode magnetostrictive readout has dispersive characteristics which effect the shape of acoustic pulses and requires linearity corrections in order to achieve maximum accuracy. To overcome this difficulty, lowest-mode torsional pulses in the magnetostrictive sense wire is used in the inventive large wire chamber.

The conventional crossed-wire plane type chamber results in an efficiency which is liable to vary appreciably over its sensitive surface because the inductance of the wire produces a nonuniform electric field in the gap when a high-voltage pulse is applied through the bus bars of each plane. Other prior arrangements in which either of two wire planes have wires parallel to each other, or one of the planes is made of a solid conducting sheet improved the pulse characteristics appreciably. However, both of these prior approaches have the obvious disadvantage that they require a larger number of gaps in order to obtain the same information on track coordinates that the crossed-wire-plane gaps achieve. These disadvantages have been overcome by charging a crossed-wire configured chamber capacity through thin aluminum planes placed closed to the wire planes, as described thereinafter.

Two embodiments of the inventive large wire chambers are schematically illustrated in FIGS. 3 and 4. The FIG. 3 embodiment provides for a decoupling of the two gaps by having separate conductors for the central planes. As shown, the FIG. 3 chamber generally indicated at 50 comprises a pair of sections or gaps indicated by legend as GAP I AND GAP ll, each being connected to a coaxial cable but electrically opposite, the coaxial cables being connected to a high-voltage pulser unit as indicated by legend. The coaxial cable connected to GAP I consists of a central high voltage electrode 51 and an outer grounded electrode 52, while the coaxial cable for GAP ll consists of a central high voltage electrode 53 and an outer grounded electrode 54, the sections or gaps I and II of the chamber 50 are similarly constructed and comprise a conventional chamber wire plane 55, a first aluminized Mylar plane 56, planes 55 and 56 being connected to a bus bar 57, a chamber wire plane 58 positioned transverse to wire plane 55, a layer of insulation 59, and a second aluminized Mylar plane 60, aluminized Mylar planes 56 and 60 being connected across a resistor 61. The charging aluminized Myler planes are constructed, for example, of 0.2-mm. Mylar and 0.0l-mm. aluminum which is strong and provides a minimum amount of material in the way of the beam particles. The charging planes 55 are electrically connected along their entire length to the bus bars 57 of their corresponding wire planes 55. In the case of GAP I, the central high-voltage electrode 51 is connected to bus bar 57 with the wire plane 58 connected to the outer grounded electrode 52, while in GAP II the inner or central electrode 53 is connected to wire plane 58 with the outer grounded electrode 54 connected to bus bar 57. The resistors 61 of GAPS I and II jointly define a termination 62.

The FIG. 4 embodiment of the inventive large wire spark chamber is utilized in sparkostrictive (nonmagnetic readout) chambers in which the decoupling is not necessary, since smaller currents are drawn during the spark. Components of FIG. 4 similar to FIG. 3 components will be given smaller reference numerals. As shown in FIG. 6, the spark chamber generally indicated at 50' comprises a pair of sections or gaps indicated by GAP I and GAP ll, each being connected to a coaxial cable but electrically opposite, the coaxial cables being connected to a high-voltage pulser unit as indicated by legend and consists of central high-voltage electrodes 51 and 53 and outer grounded electrodes 52 and 54. The sections or gaps I AND II of chamber 50' are similar in construction and comprise a chamber wire plane 55, a first charging aluminized Mylar plane 56, planes 55 and 56' being connected to a nonconductive support 63, a chamber wire plane 58 positioned transverse to wire plane 55', a layer of insulation 59', and a second charging aluminized Mylar plane 60', the first charging plane 56 of GAP I serving as the second charging plane of GAP II by the positioning of the nonconductive support 63 of GAP I in abutment with the second charging plane 56' of GAP II. With this arrangement, each of the central high-voltage electrodes 51 and 53 of the coaxial cables from the associated pulser unit are connected via a lead 64 to the charging plane 56' of GAP I which, as pointed out above, also functions as the second charging plane (60) of GAP II. The first charging plane 56 of GAP II is electrically connected to the second charging plane 60' of GAP ll via a lead 65 which is connected through a resistor 66 to the charging plane 55' of GAP I at the opposite end thereof to which the high voltage lead 64 is connected. The resistor 66'defines a termination 67 for GAPS I and II.

Since the impedance of a parallel-plate transmission line in air is Z =377( I/b, where a is the width of the gap, and b is the width of the plane, the impedance of the GAPS I and II of chamber 50 or 50' will usually be of the order of a few ohms. The low-impedance termination 62 or 67 at the far end of the chamber insures that electrical reflections are well damped, and hence that the electric field in the gap is uniform during the buildup of the spark. Furthermore, since this impedance is small compared to the spark impedance during its formation phase, it tends to minimize voltage changes that would otherwise occur if the current load on the voltage source varied appreciably due to different numbers of sparks in each event.

The total current drawn by the sparks in FIGS. 3 and 4 chambers can be limited by the use of a quenching gas such as ethyl or methyl alcohol, this being verified by tests con ducted with the results plotted to show the relative currents drawn by sparks under the same external conditions but with different amounts of quenching gas. The effect on the threshold voltage on the chamber as a function of the quenching-gas concentrations was also tested with satisfactory results. These concentrations can be easily obtained by bubbling the normal Ne-He mixture through the appropriate organic liquid maintained at a specific temperature. Since the sparks appeared to be very clean and narrow although with a much-diminished brightness relative to the pure Ne-He gas, it is feasible and convenient to limit spark currents by this method. The reduction is threshold potential as a function of quenching-gas concentration is due to the Penning effect. It was also found that the diminution of the spark current decreased the recovery time ofthe spark chambers.

The voltage pulse of the FIGS. 3 and 4 chambers can be PROVIDED by discharging a delay line of the same characteristic impedance as the chamber. Such a delay line can be made by paralleling a number of coaxial cables to give the necessary impedance. In practice, utilizing this concept, it has been found that the voltage pulses appearing on the chamber can be made satisfactorily by discharging 2 or 3 sections of an artificial delay line. FIG. 5 illustrates an embodiment use of the delay line arrangement, incorporated into the FIG. 3 chamber arrangement, where the inductance between the condensers therein is provided by a short piece of SO-ohm cable, for example. As shown in FIG. 5, wire chamber 50 comprises, as described in FIG. 3, GAP I and GAP II connected by high-voltage inner electrodes 51 and 53, respectively, and grounded through outer electrodes 52 and 54, respectively, of the associated coaxial cables, which for example are 12 ft. in length and 16 ohms resistance. Resistors 61, forming the termination 62 of FIG. 3, may be 15 ohms, for example. The high voltage electrodes 51 and 53 are each; connected to a high voltage input line 68 which terminated at the delay line circuit indicated generally at 69 and consists of a DC power supply 70 connected through a limiting resistor 71 to a high voltage lead 72 to which is connected the input line 68 to the chamber 50. A spark gap 73 is connected on one side thereof to the high- .oltage lead 72 and to ground on the opposite side. A first capacitor C1 is positioned in lead 72 intermediate the points of connection thereof with spark gap 73 and input line 68. High-voltage lead 72 is connected to an inner electrode 72' of positioned transversely to a chamber wire 81, and a local pulsed longitudinal field. The superposition ofthese two fields produces a local pulsed helical field which generates a torsional pulse provided that H is greater than H Since the a pair of coaxial cables 74 and 75, the outer electrode of the component H9 is generated by a uniform current passing cable 74 and 75 being connected to ground and interconthrough the wire 80, it is maximum at the surface and nected via a lead 76. Each of coaxial cables 74 and 75 are, for decreases to zero at the center. Thus there will be a region of example, 1% ft. long and of SO-ohm resistance. The inner electhe wire where HglS less than H, and in this region a longitutrode 72' of cable 75 is connected to an inner electrode 77 of dinal pulse will be generated. The simultaneous generation of another coaxial cable 78, the outer electrode of cable 78 being torsional and longitudinal pulses poses no difficulty, since the connected by a lead 79 to cable 75 and thus to ground. Cable detector (see FIGS. 7 and 8) can be made to pick up one or 78, for example, is also l ft. long and of SO-ohm resistance. the other uniquely.

The inner electrode 77 of cable 78 extends as indicated at 77' The mode-converter arrangement shown in FIG. 7, made by to connect with high voltage lead 72 intermediate capacitor soldering short pieces 82 and 83 of nickel wire or ribbon at the Cl and the point of connection with spark gap 73. A second end of the sense wire 80 with pickup coils 84 and 85 wrapped capacitor C2 is connected intermediate the extended portion about the nickel ribbons 82, detects only torsional pulses with inner electrode 77' of cable 78 and the point of interconneca high degree ofdiscrimination against longitudinal pulses. tion of inner electrodes 77 and 72, while a third capacitor C3 Alternatively, as shown in FIG. 8, the coil pickup arrangeis positioned in extended electrode 77 intermediate the point ment commonly used for detection of longitudinal pulses can of connection with capacitor C2 and cable 78, such that be used also, and consists ofa DC power source 86 connected capacitors C1, C2 and C3 are connected in parallel with the in series with a ferromagnetic wire 87 having a damping pad coaxial cables 74, 75 and 78 connected in series. Capacitors 88 at each end thereof with a transmitting coil 89 and a receiv- C1, C2 and C3 are respectively, for example, 3400 pf. 5000 ing coil 90 wrapped about wire 87 intermediate the damping pf. and 6800 pf. pads. If the coil 89 is biased by a longitudinal DC magnetic Tests were conducted on a pair of wire chambers consisting field, it detects the longitudinal pulse; if there is no DC comof two gaps each of the type illustrated in FIG. 3, and in which ponent of magnetic field in the portion of the sense wire 87 in the two ground planes of each chamber had wires oriented the coil 89 (i.e., no bias magnet) the longitudinal pulses are vertically and horizontally, while the two high-voltage planes not detected, whereas the torsional pulses are detected by the in the middle had wires oriented at 0" relative to the vertical inverse Wiedemann effect. This inverse effect is the generadirection. The gap widths were 1 cm., and the external dimention of a voltage signal by a time-varying helical magnetic sions of the chamber were 1.5 meters wide and 2 meters long. field. In reality, various torsional pulse modes may be excited It was found that the multiple-track efiiciency obtained from by the pulsed helical field. However, the lowest mode can althe two magnetostrictive chambers ranged from about 90l00 ways be selected by choosing the wire diameter so it is the only percent. The multiple-track events, in these tests, were one that will propagate with slight attenuation. The preferred generated by electron-positron background pairs traversing sense wire for the FIG. 3 embodiment is a wire of hard-drawn the chambers during the 1.5-used beam spill of the known ac- Elinvar Extra (an alloy of iron, nickel, chromium and titanium celerator. used in commercial delay lines).

The magnetostrictive-delay-line readout method, as exem- Thus, as illustrated by FIGS. 3-8, large wire chambers can plified in FIG. 5, when utilized with smaller chambers uses be built with uniform, high multiple-track efficiency by charglongitudinal pulses in the sense wire. As is well known in ing the capacity of the chamber through aluminum backing acoustic theory, this type of pulse transmission has dispersive plates and terminating the chamber in its characteristic impropagation properties and hence poses some practical limitapedance. Since this is of the order of a few ohms, the effect of tions on the length of the sense wire that can be used. Some of the spark currents on the voltage wave form is small, and the properties of longitudinal pulses and lowest-order torhence there is a uniform efficiency for multiple tracks. The sional pulses are listed in Table 1 set forth below: use of torsional pulses on the readout line permits a high accu- TABLE 1 Longitudinal Torsional Pulse generation Joule efiect Wiedemann efiect. Pulse detection Inverse Joule (Villari) efiect Inverse Wiedemann effect.

.Jongitudinal phase velocity in infinite medium C1,= u CT= ('5 =vel0city of transverse Waves.

1r o' T'- Phase velocity V in wire of radius 9, wavelength A V1; 0;,( 1- A2 VT= CT (for lowest mode).

Wire radius r f 5'14VT or useful pulse propagation r 0.1 T f- (for lots est mode).

11 X, Lame constants, Er,=Youngs modulus of elasticity, =density x lateral contraction of mammal b 2( longitudinal extension S From Table 1 It can be seen that the dispersive efiects can racy of park position |0ati0n algng the hamber's entire be minimized by choosing a sense-wire diameter small comlength. pared to the mean effective wave length of the pulse. In prac- Therefore, the present invention provides wire spark chamtice utilizing the inventive FIG. 3 embodiment, a 0.15-mm.- bers which are self-triggering and particularly adapted for use dia. Vacoflux Fe-Co sense wire has been used, and found to be with low energy, neutral particles and which provide a high a suitable compromise between a satisfactory degree of uniform efficiency for registering multiple tracks in large surdispersion and signal strength. In tests conducted there was a face area chambers. noticeable degradation in the pulse shape at distances greater Although particular embodiments of the inventive concept than 2 meters. Thus for larger chambers the use of torsional have been illustrated and described, modifications will pulses becomes worthwhile, since the lowest-mode pulses become apparent to those skilled in the art, and it is intended have no dispersion and they can be generated in wire chamto cover in the appended claims all such modifications as bers in the same configuration as used for longitudinal pulses. m i hin h pir n PE 0f he invention.

The method of generating torsional pulses in wire chambers We Claiml involves the use of the Wiedemann effect as shown in FIG, 6 l. A spark chamber for detecting radiation in combination The torsional pulses are generated by a combination of a steady-state azimuthal magnetic field through a sense wire 80,

with magnetostrictive readout means, said spark chamber comprising a central electrode means mounted for connection to a high voltage power source. a pair of outer electrode means positioned at a predetermined distance on opposite sides ofsaid central electrode means and mounted for connection to ground, said chamber being filled with a predetermined gas mixture a high voltage power source operatively connected to said central electrode means, preamplifier means operably connected between said central electrode means and said power source, linear amplifier means operably mounted to receive an input from said preamplifier means and to direct an output into a logic circuit means and a spark chamber pulser means connected between an output of said logic circuit means and said central electrode means.

2. The spark chamber defined in claim 1, wherein said central electrode means consists of a wire plane composed of a plurality of equally spaced small diameter wires mounted on an insulator frame, and wherein each of said outer electrode means consists of a wire plane composed of copper etched Mylar,

3. The spark chamber defined in claim 2, wherein said gas mixture is at atmospheric pressure and composed of 90 percent Ne- 10 percent He saturated at room temperature with ethyl alcohol.

4. The combination defined in claim ll additionally comprising: a current limited resistor means mounted between said central electrode means and said power source, wherein said preamplifier is a voltage-sensitive preamplifier, capacitor means mounted between said preamplifier means and said central electrode means, wherein said linear amplifier is a variable gain linear amplifier, and a series spark gap means mounted between said central electrode and said spark chamber pulser means for decoupling said pulser means from said capacitor means.

5. The combination defined in claim 4, additionally including a back-to-back diode arrangement mounted intermediate said capacitor means and said preamplifier means for protecting said preamplifier means during sparking, resistor means positioned intermediate said capacitor means and said diode arrangement for limiting current through the diode arrangement, a capacitor connected to ground and connected intermediate said power source and said current limiting resistor means for eliminating power supply ripple, and a resistor connected on the ground side of said capacitor and intermediate said capacitor means and said diode current limiting resistor forming a resistive ground connection 6. The spark chamber defined in claim 1, wherein said central electrode means comprises a pair of electrodes each adapted for connection to said high voltage power source; one of said pair of electrodes consisting of a wire plane composed of a plurality of equally spaced small diameter wires, an aluminized Mylar plane, and a layer of insulation positioned intermediate said wire plane and said aluminized Mylar plane; the other of said pair of electrodes consisting of a wire plane ill composed of a plurality of equally spaced small diameter wires positioned transversely to the wires of said wire plane of said one of said pair of electrodes, an aluminized Mylar plane, and a conductive bus bar means electrically interconnecting said wire plane and said aluminized Mylar plane; wherein one of said pair of said outer electrode means is constructed substantially identical to said one of said pair ofelectrodes comprising said central electrode means; and wherein the other of said pair of said outer electrode means is constructed substantially identical to said other of said pair of electrodes comprising said central electrode means; said one of said pair of outer electrodes by resistive means interconnecting the aluminized Mylar planes thereof, and said other of said pair of outer electrode means being connected to said one of said pair of electrodes by resistive means interconnecting the aluminized Mylar planes thereof; each of said outer electrode means being positioned in a spaced parallel location with respect to the associated electrode of said central electrode means so as to define a gap therebetween and said resistive means forming terminations at the opposite end of said planes from the respective point of connection of said central and outer electrode means to high voltage and ground 7. The spark chamber defined in claim 1, wherein said central electrode means comprises an aluminized Mylar plane, a first wire plane positioned on one side of said aluminized Mylar plane, a layer of insulation material positioned between said planes, a second wire plane positioned on the opposite side of said aluminized Mylar plane, and an electrically conductive bus bar means connecting said second wire plane and said aluminized Mylar plane, each of said wire planes being composed of a plurality of equally spaced small diameter wires and said first wire plane being mounted transversely to said second wire plane; wherein one of said pair of outer electrodes comprises a wire plane composed of a plurality of equally spaced small diameter wires, an aluminized Mylar plane, and a layer of insulation material positioned intermediate said planes, said wire plane being positioned parallel to and trans versely with respect to said first wire plane of said central electrode means and spaced therefrom to define a gap therebetween; wherein the other of said pair of outer electrodes comprises a wire plane composed of a plurality of equally spaced small diameter wires, an aluminized Mylar plane, and electrically conductive bus bar means positioned intermediate each of said planes and connected thereto, said wire plane being positioned parallel to and transversely with respect to said second wire plane of said central electrode means and spaced therefrom to define a gap therebetween, said aluminized Mylar planes of each of said outer electrode means being electrically interconnected and connected via a resistor means to said central electrode means at the end thereof opposite the end of said central electrode means adapted to be connected to a high voltage power supply. 

1. A spark chamber for detecting radiation in combination with magnetostrictive readout means, said spark chamber comprising a central electrode means mounted for connection to a high voltage power source, a pair of outer electrode means positioned at a predetermined distance on opposite sides of said central electrode means and mounted for connection to ground, said chamber being filled with a predetermined gas mixture a high voltage power source operatively connected to said central electrode means, preamplifier means operably connected between said central electrode means and said power source, linear amplifier means operably mounted to receive an input from said preamplifier means and to direct an output into a logic circuit means and a spark chamber pulser means connected between an output of said logic circuit means and said central electrode means.
 2. The spark chamber defined in claim 1, wherein said central electrode means consists of a wire plane composed of a plurality of equally spaced small diameter wires mounted on an insulator frame, and wherein each of said outer electrode means consists of a wire plane composed of copper etched Mylar.
 3. The spark chamber defined in claim 2, wherein said gas mixture is at atmospheric pressure and composed of 90 percent Ne-10 percent He saturated at room temperature with ethyl alcohol.
 4. The combination defined in claim 1 additionally comprising: a current limited resistor means mounted between said central electrode means and said power source, wherein said preamplifier is a voltage-sensitive preamplifier, capacitor means mounted between said preamplifier means and said central electrode means, wherein said linear amplifier is a variable gain linear amplifier, and a sEries spark gap means mounted between said central electrode and said spark chamber pulser means for decoupling said pulser means from said capacitor means.
 5. The combination defined in claim 4, additionally including a back-to-back diode arrangement mounted intermediate said capacitor means and said preamplifier means for protecting said preamplifier means during sparking, resistor means positioned intermediate said capacitor means and said diode arrangement for limiting current through the diode arrangement, a capacitor connected to ground and connected intermediate said power source and said current limiting resistor means for eliminating power supply ripple, and a resistor connected on the ground side of said capacitor and intermediate said capacitor means and said diode current limiting resistor forming a resistive ground connection.
 6. The spark chamber defined in claim 1, wherein said central electrode means comprises a pair of electrodes each adapted for connection to said high voltage power source; one of said pair of electrodes consisting of a wire plane composed of a plurality of equally spaced small diameter wires, an aluminized Mylar plane, and a layer of insulation positioned intermediate said wire plane and said aluminized Mylar plane; the other of said pair of electrodes consisting of a wire plane composed of a plurality of equally spaced small diameter wires positioned transversely to the wires of said wire plane of said one of said pair of electrodes, an aluminized Mylar plane, and a conductive bus bar means electrically interconnecting said wire plane and said aluminized Mylar plane; wherein one of said pair of said outer electrode means is constructed substantially identical to said one of said pair of electrodes comprising said central electrode means; and wherein the other of said pair of said outer electrode means is constructed substantially identical to said other of said pair of electrodes comprising said central electrode means; said one of said pair of outer electrodes by resistive means interconnecting the aluminized Mylar planes thereof, and said other of said pair of outer electrode means being connected to said one of said pair of electrodes by resistive means interconnecting the aluminized Mylar planes thereof; each of said outer electrode means being positioned in a spaced parallel location with respect to the associated electrode of said central electrode means so as to define a gap therebetween and said resistive means forming terminations at the opposite end of said planes from the respective point of connection of said central and outer electrode means to high voltage and ground.
 7. The spark chamber defined in claim 1, wherein said central electrode means comprises an aluminized Mylar plane, a first wire plane positioned on one side of said aluminized Mylar plane, a layer of insulation material positioned between said planes, a second wire plane positioned on the opposite side of said aluminized Mylar plane, and an electrically conductive bus bar means connecting said second wire plane and said aluminized Mylar plane, each of said wire planes being composed of a plurality of equally spaced small diameter wires and said first wire plane being mounted transversely to said second wire plane; wherein one of said pair of outer electrodes comprises a wire plane composed of a plurality of equally spaced small diameter wires, an aluminized Mylar plane, and a layer of insulation material positioned intermediate said planes, said wire plane being positioned parallel to and transversely with respect to said first wire plane of said central electrode means and spaced therefrom to define a gap therebetween; wherein the other of said pair of outer electrodes comprises a wire plane composed of a plurality of equally spaced small diameter wires, an aluminized Mylar plane, and electrically conductive bus bar means positioned intermediate each of said planes and connected thereto, said wire plane being positioned parallel to anD transversely with respect to said second wire plane of said central electrode means and spaced therefrom to define a gap therebetween, said aluminized Mylar planes of each of said outer electrode means being electrically interconnected and connected via a resistor means to said central electrode means at the end thereof opposite the end of said central electrode means adapted to be connected to a high voltage power supply. 